Potential coupling of intramolecular to intermolecular modes: an ab initio study of the amino inversion and van der Waals motions in the aniline-argon complex

In this paper, we present a description of the vibrating aniline-argon (An-Ar) van der Waals complex in its electronic ground state by using second order Moller-Plesset (MP2) theory to elucidate the key factors which govern the configuration of this complex. The interaction between the intramolecular mode associated to the inversion motion of the amino group and the van der Waals bending mode involving the motion of the Ar atom in the direction toward the nitrogen atom, has been modeled. The ab initio results indicate not only that there is a significant coupling between the two motions, in agreement with experimental findings on vibrational predissociation, but also that the interaction between the Ar atom and the nitrogen lone pair governs the complex topology of this four-dimensional potential energy surface.